Conventionally, refrigeration apparatuses such as air conditioners, in which chlorofluorocarbon or an alternative for chlorofluorocarbon is used as a refrigerant, are widely used. However, when such refrigerants are released into the atmosphere, they cause direct ozone depletion and have high global warming potentials. In view of these, air conditioners have been proposed in which a natural refrigerant such as water, carbon dioxide, or hydrocarbon is used as a refrigerant having a very low impact on the global environment. For example, Patent Literature 1 discloses an air conditioner 100 as shown in FIG. 3, in which water is used as a refrigerant.
When water is used as a refrigerant for an air conditioner, the refrigerant in a low pressure and low density state flows in the system due to the physical properties of water. Therefore, the volumetric flow rate of the refrigerant to be compressed and the pressure ratio in a compressor need to be significantly increased. In the air conditioner 100 disclosed in Patent Literature 1, a Roots-type positive displacement compressor 110 is used as the compressor. Cooling operation and heating operation can be switched by switching the rotational direction of the Roots-type rotary compression means between the forward direction and the reverse direction.
Specifically, the air conditioner 100 includes a first casing 101 and a second casing 102 that retain water. The air conditioner 100 further includes an indoor-side circulation path 120 that allows the water in the first casing 101 to circulate via an indoor heat exchanger 121 and an outdoor-side circulation path 130 that allows the water in the second casing 102 to circulate via an outdoor heat exchanger 131. The upper part of the first casing 101 and the upper part of the second casing 102 are connected by a first communication path 103, and a compressor 110 is provided on this first communication path 103. The lower part of the first casing 101 and the lower part of the second casing 102 are connected by a second communication path 104.
In the cooling operation, the compressor 110 rotates in the forward direction so as to allow water vapor to flow in a direction indicated by solid arrows, and the first casing 101 functions as an evaporator and the second casing 102 functions as a condenser. Cold water is produced in the first casing 101, and this cold water is supplied to the indoor heat exchanger 121. Thus, the cooling operation is performed. On the other hand, in the heating operation, the compressor 110 rotates in the reverse direction so as to allow water vapor to flow in a direction indicated by dashed arrows, and the second casing 102 functions as an evaporator and the first casing 101 functions as a condenser. Hot water is produced in the first casing 101, and this hot water is supplied to the indoor heat exchanger 121. Thus, the heating operation is performed.